The All New Grandeur is trending as a luxury sedan that provides the best travel experience; It greatly satisfied customers with excellent riding comfort and quietness that exceeded expectations. Here, senior researcher Kang-wook Jeon from the R&H test team, who coordinated the overall ride comfort of The All New Grandeur, and researcher Sung-rock Jung, from the noise and vibration test team, who realized a high level of quietness, explained: how they perfected the high-quality ride comfort and quietness of The All New Grandeur.
Q. The Grandeur is everyone’s favorite best-selling car. Which part of the suspension setup was considered to appeal to a wide customer base?
Jeon | The All New Grandeur is the successor of the Grandeur, inheriting its reputation and heritage. In particular, pursuing innovation while retaining the sophistication of its predecessor is the characteristic of this All New Grandeur. So we developed it with a focus on luxurious ride comfort and driving texture, so that everyone from the younger generation to active seniors can be satisfied.
Q. A well-designed chassis is the basis for excellent ride comfort. Now, tell us about The All New Grandeur Chassis.
Jeon | The car chassis is like the skeleton of the human body. The stronger the chassis, the better the ability to absorb and offset external shocks. The advantage of the Hyundai Motor Group’s third-generation platform applied to The All New Grandeur is that it has a robust structure.
For example, the square subframe, one of the main features of the 3rd generation platform, has been extended in front and rear length compared to the previous one, improving structural safety. The subframe fixes the suspension to eliminate unnecessary vibration, and the higher its rigidity, the better the ride comfort. In addition, the suspension, which plays the same role as our body joints, is designed to optimize handling performance, steering texture, straightness, and ride comfort.
One of the results of the optimized suspension design is that the gap between the upper arm and the lower arm is widened from 170mm to 177.6mm. The upper and lower arms make the wheel broader and more stable, improving safety and handling performance. Also, one of the major changes in the third-generation platform suspension is to improve ride comfort, by setting the vertical angle of the rear damper to 1.9° and more effectively suppressing unnecessary vertical movement of the body.
Q. What part did you focus on for a comfortable ride?
Jeon | The All New Grandeur houses up to 20-inch wheels. This means that the tire sidewall, which absorbs road shock, is that thin. Under these conditions, developers have considered various ways to realize a comfortable ride. First, the minimized weight of the wheel and tire reduced the unsprung mass. In addition, by lowering the tire air pressure, it helped the thin tires absorb shock smoothly. Then, considering the bumpy road conditions, we optimized the main bushings on the suspension. This model is equipped with new technologies such as a frequency-sensitive high-performance shock absorber (SDC III) that actively suppresses rebound, and a preview ECS that adjusts damping force by referring to road surface information in front is also an optional feature.
Q. What specifically does bushing optimization mean?
Jeon | Since bushings have to absorb shock at the connection part of the car body or suspension, proper physical properties are essential. Bushings that are too soft not only destabilize the movement of the vehicle, but also cause unnecessary movement of the body, deteriorating ride quality. Of course, bushings that are too stiff also lead to poor ride quality. For this reason, proper bushings are very important.
Therefore, we developed The All New Grandeur by considering both the effect of the front wheel bushings on the rear wheels and, conversely, the effect of the rear wheel bushings on the front wheels, while considering the ride comfort of the entire vehicle. Through this process, we optimized the characteristics of the G bushings, trailing arm bushings, bump stoppers, stabilizer bushings, and subframe hydro bushings mounted on the back of the lower arm.
Q. How are hydro bushings attached to the subframe different from rubber bushings?
Jeon | In order to achieve a smooth ride, it is important to gently absorb large shocks and minimize aftershocks (small vibrations). But rubber bushings cannot do both; For example, if soft bushings are used to gently absorb large impacts, the aftershock cannot be effectively dealt with. However, since hydro bushings can effectively reduce excitation by increasing the damping force for a specific frequency (vibration), they satisfy both characteristics that seem incompatible with each other. Hydro bushings consist of a fluid and an orifice (fluid passage), and absorb impact energy by utilizing the fluid resistance generated as the fluid moves through the orifice.
Q. What is the frequency-sensitive high-performance shock absorber housed in The All New Grandeur?
Jeon | As is well known, springs and shock absorbers complement each other. While the spring repeats contraction and relaxation to convert road impact into kinetic energy, the shock absorber, which tries to maintain a constant length, suppresses this continuous movement of the spring to quickly stabilize the body.
The frequency-sensitive high-performance shock absorber goes one step further. The rebound phenomenon - the repeated stretching and compression of the spring - is controlled by dividing it into two situations: large shock (low frequency vibration less than 5Hz) and residual vibration (high frequency vibration more than 10Hz). As a result, the low damping force smoothens the movement of the body when the road surface is quickly crossed, and the strong damping force quickly suppresses the aftershock when small vibrations are transmitted, realizing a clean and stable ride.
Q. Please explain the operating principle and control effect of the optional Preview Electronically Controlled Suspension.
Jeon | Electronically controlled suspension with road preview utilizes the front camera and navigation map information to recognize bumps or potholes in advance and provides optimal ride comfort with appropriate suspension control. Before passing a bump, the damping force is lowered to gently absorb road shock. And after passing through it, the damping force is increased again to suppress the pitching phenomenon in which the vehicle swings forward/backward. As such, the principle of electronically controlled suspension with road preview is to recognize a large impact from the road surface in advance and change the damping force of the suspension accordingly.
Q. In addition to the normal mode, the electronically controlled suspension with road preview also supports a sport mode with strong damping power. How does damping force control vary according to each mode?
Jeon | While the normal mode focuses on a comfortable and smooth ride, the sport mode controls vehicle behavior with stronger damping force to achieve better cornering and handling performance. This is thanks to optimal tuning among various handling test processes to improve road followability and limit performance. For reference, the damping force in sports mode is about 20 to 30% stronger than in normal mode.
Q. How was the bump stopper of The All New Grandeur optimized?
Jeon | If you go over a speed bump quickly enough for the shock absorber to fully contract, you’ll feel the road shock being transmitted to the wheels → the strut tower → the entire body. A bump stopper is a shock absorber mounted on a shock absorber column. This is an automobile part that secures the minimum ride quality by absorbing the shock that the spring and shock absorber could not handle in such a situation.
When the spring and shock absorber contract, the bump stopper induces resistance to effectively absorb large shocks. Such a bump stopper requires a delicate design because its resistance characteristics vary depending on its shape. The All New Grandeur was able to realize a smoother and more seamless ride by reducing the length of the bump stopper and utilizing optimized physical properties.
Q. What was the focus of the NVH performance of The All New Grandeur?
Jung | First of all, we wanted to enhance the feeling of separation between the outside and the inside. In addition, the NVH performance of The All New Grandeur was developed with the goal of quietness in harmony with the engine sound, rather than simply creating a quiet environment. This is because we wanted to provide customers with a pleasant moving experience that goes beyond the limits of the interior with exciting driving performance and high level of quietness.
Q. What is the main feature that helped quietness of The All New Grandeur?
Jung | In order to improve quietness, gaps between the car bodies should be closed to reduce noise inflow, and interior noise should be minimized with sound-absorbing materials. The All New Grandeur secured high-level NVH performance by strengthening sound insulation and sound absorbing materials for each part in order to respond to major noise sources - engine noise, road noise, wind noise, etc. Specifically, road noise was reduced by utilizing detachable floor carpets and sound-absorbing tires, and wind noise was reduced by laminated glass(double-bonded sound-insulating) and enhanced weather strip performance.
Q. How is the detachable floor carpet different from the current floor carpet?
Jung | Floor carpet is an interior material that reduces noise and vibration transmitted through the floor. Since the current floor carpet consists of a sound-absorbing layer that absorbs sound and a sound-insulating layer that blocks noise, the weight increases as the NVH performance increases. On the other hand, the newly developed detachable floor carpet has a structure in which the sound-absorbing layer and the sound-insulating layer are divided, so it can cover more floor area and has better NVH performance. In other words, the advantage of the detachable floor carpet is to minimize the increase in weight due to the improved NVH performance.
Q. How do sound-absorbing tires reduce road noise?
Jung | Acoustic tires greatly reduce road noise from the wheels of a car; This is because the sound-absorbing material attached to the inside of the tire absorbs the resonance sound of 4 to 5dB that occurs in the empty space between the tire and the wheel. This is the most efficient noise reduction method as it works close to the noise source. For reference, The All New Grandeur, like a luxury sedan, housed sound-absorbing tires on all trims.
Q. In general, frameless doors are known to have a difficult structure to secure NVH performance. But the All-New Grandeur is quieter than its rival model with framed doors. How did you overcome the disadvantages of frameless doors?
Jung | Road noise and wind noise are introduced into two main routes: either a part of the car body acts as a medium for noise, or the noise is transmitted directly through a passage that penetrates the exterior and interior. In The All New Grandeur, the gap between the door and the body was reduced to secure the NVH performance of the frameless door. In addition, noise transmission through the glass was suppressed by applying laminated glass(double-bonded sound-insulating) extensively.
Q. How did you increase the airtightness of the frameless door?
Jung | To increase airtightness, we carefully closed the gaps (parting lines) between the outer panels around the door with rubber strips, while wrapping the door opening with three layers of weather strips. In addition, the watertight performance has been reinforced by using a multi-blocking structure that functions as a water trap in the weather strip. In other words, the sealing performance is enhanced so that noise does not flow into the door gap. In addition, the inside belt weather strip, which is in contact with the bottom of the side glass, is made of EPDM (Ethylene-Propylene Diene Monomer), a synthetic rubber material that is resistant to cold and heat, ensuring durability that maintains NVH performance even after a long time.
Q. How effectively does laminated glass(double-bonded sound-insulating) reduce noise?
Jung | Laminated glass(double-bonded sound-insulating) has excellent NVH performance thanks to a special film that absorbs noise and vibration between two sheets of glass. By using laminated glass(double-bonded sound-insulating) for the windshield, side glass, and rear quarter glass in The All New Grandeur, it was possible to reduce noise by 2.5dB (compared to single-layer glass of the same thickness). Instead of being single-layered, the delta glass of the first-row door was increased to 6mm in thickness to achieve the same NVH performance as laminated glass(double-bonded sound-insulating).
Q. What other creative ideas were used to enhance NVH performance?
Jung | Besides the massive use of laminated glass(double-bonded sound-insulating) to enhance NVH performance, there are additional methods using glass; When the window is completely closed, the area of the glass window embedded inside the door is widened to reduce noise intake. Leakage noise refers to the noise generated when outside air flows into the vehicle due to the pressure difference between the inside and outside of the vehicle. Focusing on the fact that the tip of the inside belt weather strip is the main cause of this noise, the leakage noise was prevented by widening the area of the side window hidden inside the door. Thanks to such attention to invisible places, I think that The All New Grandeur was able to provide the best smooth ride.
Photography by Choi Dae-il, Kim Bum-seok
HMG Journal Operation Team
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